Self-indicating plug fuse



Nov. z2, 1938.

sa@ e R. w. KING 2,137,342

SELF INDICATING PLUG TUSE Filed Oct. 2, 1937 Patented Nov. 22, 1938UNITED I STATES PATENT OFFICE 6 Claims.

This invention relates to fuse plugs for electrical circuits, and moreparticularly to selfindicating fuse plugs, so-called, constructed toindicate when they are blown.

In the drawing of one embodiment of my novel invention selected forillustration and description herein:

Fig. 1 is a plan;

Fig. 2, a vertical section on, the line 2-2, Fig. 1, with the parts innormal position;

Fig. 3, a similar view with the parts in abnormal or inoperativeposition, and indicating that the fuse has blown;

Fig. 4, a horizontal section on the line 44, Fig. 2, looking down; and

Fig. 5, a detail of a portion of Fig. 4, on an enlarged scale.

Referring first to Figs. l and 2 oi the drawing, -my novel fuse plugcomprises a chambered shell I, of any suitable material, as hard rubber,porce lain and the like, with an opening 2 at its upper end.

The lower end of the shell is threaded as at 3, 'to engage the usualblock or other receptacle therefor, on a support not shown, and isprovided with a similarly shaped conductor sleeve 4 of metal or othersuitable material, to conduct the current from the block to the fuse,and it also is fashioned to carry the cap member 5 for the shell, withthe conductor post 6.

This post carries, in turn, the conveniently shaped fuse element 1, ofsuitable material, as metal, and the fuse is secured between` the loweredge of the shell, a gasket 8 and the cap 5, with the opposite fuse endsoldered or suitably secured to the conductor sleeve 4 at 9.

Adjacent the bridge portion I0 of the fuse, there is mounted an invertedU-shaped strip of any suitablegas-producing, inflamm-iable anddeagrating, button-ejecting material I2, which is retained in closeproximity to the fuse 'l by being secured at its ends between the gasket8 and the cap 5.

The strip I2 should not only be of an inflammable and deagrating nature,but should also be of such chemical composition as to include sufficientoxygen to support the combustion of the strip in the absence ofatmospheric oxygen, for it may be that there will be insufficientatmospheric oxygen confined in the plug to consume any appreciablequantity of a combustible material. Furthermore, not only should themate rial I2 be of such nature as to ignite and burn readily, ordeflagrate in its chamber I9 when ignited by the flash from the fuse 1when it blows,

but the button projecting member should also possess the characteristicof producing, in its combustion, such a large volume of gases as tocause them, when confined in the plug, to develop sufiicient pressure toforce a button I4 forward and project it through the opening 2, whichalso serves as an exit for the escape of air from the plug when itejects the button. Cellulose nitrate is satisfactory under allprevailing conditions in which it has been tried. I can think of nocondition where it would not answer the purpose satisfactorily, unlesswhere the current was flowing through the fuse in such quantity andunder such continuous use as to raisel the temperature of the chamber ofthe plug to a degree suflicient to cause decomposition of the cellulosenitrate. Such a condition is not to be anticipated, and would be mostunusual, and probably due to faulty construction.

If one wished to guard against such extreme or unexpected conditions, agas-producing, inflammable strip of material, analogous in all essentialrespects to cellulose nitrate, but less responsive to a long-continued,high degree of heat, such as a strip of heavy paper, carrying a coatingof granules of gunpowder, might be used. This would be a naturalsubstitute for the nitrate cellulose in its form of action, but not soconvenient for use, as it would need to be specially prepared.

The button I4 should be provided with a cup shaped or othersuitably-shaped base I5, as a contact area for the gas tol ensure theprojection of the button. In this instance, I have provided the basewith a skirt or housing I6 to more reliably ensure the action of the gason the button by reducing the volume of the combustion chamber to asmaller area. The clearance space I'I between the housing I6 and theshell I may be closed practically air-tight by sealing it with a washeror bushing I8 on the housing outer wall, thus providing a closedcombustion chamber I9, and also ensuring that the button will remain inany adjusted position in the shell.

The button may be of the same color and material as the shell, b-utpreferably has its side wall 28 of a contrasting color, as blue, forinstance, to attract attention.

It is a very desirable qualification to the successful operation of adevice of this kind that the gas-producing, inflammable and deflagratingmaterial I2, partially surrounding the bridge portion I0 of the fuse,shall unfailingly ignite the instant the fuse blows. Now it is knownthat a sharp point or edge of any combustible material is more readilyignited than is a ilattened or smooth surface of the same. Therefore, inrecognition of this fact, that portion of the strip I2, if of a materialhaving a smooth surface, immediately surrounding the bridge portion ofthe fuse is so pierced as to create a number of sharp points or teeth 2land edges, all projecting inwardly and thence effectively subjected tothe ame and molten metal of the arc formed at the instant of the blowingof the fuse.

The button I6 may be provided with guides 22 to retain the element I2 inproper position.

My invention is not restricted to the particular embodiment thereofherein described and illustrated, but may bemodied in many details,without departing from the spirit of the claims, and within the scopethereof.

I claim:

1. A self-indicating chambered fuse plug with a fuse and conductormember therefor in the chamber, the chamber having one end closed with aconductor member therein, an opening in one plug end, a button movabletherein, and a pressure producing member in the chamber and ignitable bythe fuse to produce vapor to project the button through said opening.

2. A self-indicating fuse plug with a chamber and an opening thereto, afuse therein with conductor members therefor, a button with an eX-panded inner end movable in said opening, and a gas-producing member insaid plug and ignitable by the fuse when it blows, to project the buttonthrough said opening.

3. A self-indicating fuse plug with a chamber having a fuse therein, andconductor members therefor, an opening in one plug end, a housing in theshell chamber with a bushing and having a button thereon with adistinctively colored end projectable through said opening, agas-producing member in said plug adjacent the fuse and ignitablethereby when it blows, to move said housing and project said button endthrough the opening.

4. A self-indicating fuse plug comprising a shell with a chamber havingan opening in one end, a housing with a button thereon in the shell, thehousing tting closely in the chamber and movable therein,receptacle-engaging means on the plug, with a conductor member connectedthereto, a fuse-carrying conductor member on said shell end with a fusethereon connected also to the first-named conductor means; arough-surfaced, gas producing member adjacent said fuse and ignitable bythe blowing of the fuse to create pressure to project said button fromthe shell chamber and through said opening.

5. A self-indicating fuse plug comprising a shell with a chamber havingan opening in one end, a housing with a button thereon in the shell, thehousing fitting closely in the chamber and movable therein,receptacle-engaging means on the plug, with a conductor member connectedthereto, a fuse-carrying conductor member on said shell end with a fusethereon connected also to the first-named conductor means; a toothedgasproducing member adjacent said fuse and ignitable by the blowing ofthe fuse to create pressure to project said button from the shellchamber and through said opening.

6. A self-indicating fuse plug with a chamber and an opening thereto, afuse therein with conductor members therefor, a button with an expandedinner end movable in said opening, and a cellulose nitrate member insaid plug and ignitable by the fuse when it blows, to project the buttonthrough said opening.

REGINALD W. KING.

